1. Field of the Invention
The present invention relates generally to a socket. More particularly, the present invention relates to a socket, a method for manufacturing the socket, a device, and a method for compensating for differing coefficients of thermal expansion between a surface mounted socket and a printed circuit board.
2. Description of the Related Art
Dual in-line memory module (DIMM) sockets are used in computers to electrically connect memory modules to a processor package that is mounted on a printed circuit board. Currently, pins are the most popular means for physically attaching dual in-line memory module sockets to circuit boards. The pins fit through holes in the circuit board, and, typically, the pins are either soldered or press-fitted to the board, thereby forming a physical connection between the dual in-line memory module socket and the printed circuit board. The physical connection allows electrical signals to pass between the memory module residing in the dual in-line memory module socket and the processor package mounted on the printed circuit board. However, recent increases in processor performance are requiring higher electrical signal speeds to pass within a memory bus. As a result, electrical performances of the present dual in-line memory module socket pin design are insufficient. Therefore, the industry is moving towards new surface mounted lead designs to attach dual in-line memory module sockets to the circuit boards.
However, many manufacturing difficulties exist with surface mounted dual in-line memory module socket designs. The greatest challenge surrounds the differences in the coefficients of thermal expansion (CTE) between the dual in-line memory module socket housing material and the printed circuit board material. In manufacturing, a soldering reflow process is used to attach the dual in-line memory module socket to the circuit board. The soldering reflow process exposes the dual in-line memory module socket and the circuit board to extremely high temperatures. Because of the differences in the coefficients of thermal expansion, the dual in-line memory module socket housing and the circuit board expand at different rates during heating. Consequently, the circuit board tends to warp and create stress on the solder joints between the circuit board and the dual in-line memory module socket. The solder joint stress causes the joints to crack, which eventually results in broken electrical connections and memory bus failures after multiple on and off cycles.
Several solutions currently exist to address the warping problem arising from the differences in the coefficient of thermal expansion. One solution is to change the dual in-line memory module housing material to a material that has a similar coefficient of thermal expansion as the circuit board. Another solution is to apply a mechanical fixture and utilize thermal management techniques during the solder reflow process to control the warping. Yet another solution includes flattening the warped circuit board using a clamping fixture and an extended high temperature annealing of the solder joint stress. However, due to either unacceptable results or significant additional manufacturing costs, none of the solutions have been attractive.